1. Field of the Invention
The present invention relates to a sensor, a rolling bearing with a sensor and a rotating support apparatus with sensor which are utilized for causing a housing or a suspension system—which remains stationary even at time of use—to rotatably support wheels of a railroad vehicle, those of an automobile, or a rotating shaft of a rolling mill for metal working, as well as being utilized for detecting the status of the rolling bearing or that of the rotating support apparatus. The rolling bearing and the rotating support apparatus are effective for checking an abnormality in the rolling bearing, by means of detecting, e.g., the rotation speed of wheels or rotating shaft and the status of the rolling bearing (i.e., the temperature or vibration of the rolling bearing).
2. Description of the Related Art
A rolling bearing unit is used, for instance, for causing a housing fastened to a railroad vehicle to rotatably support railroad wheels. In order to determine the traveling speed of the railroad vehicle or to effect skidding control for preventing occurrence of unbalanced wear in the wheels, the rotational speed of the wheels must be detected. Moreover, in order to prevent occurrence of seizing up of the rolling bearing unit, which would otherwise be caused as a result of an abnormality having arisen in the rolling bearing unit, the temperature of the rolling bearing unit must be detected. To these ends, supporting of the wheels rotatable with respect to the housing, detection of rotation speed of the wheels, and detection of temperature of the rolling bearing unit have recently been effected through use of a rotating support apparatus with sensor, the apparatus being constituted by means of incorporating a rotation speed sensor and a temperature sensor into the rolling bearing unit.
FIGS. 59 and 60 show the structure of a related-art sensor-equipped rotating support apparatus for use with a railroad vehicle. An axle shaft 1 acts as a rotating shaft which rotates at the time of use while having an unillustrated wheel fixedly supported thereon. In order to achieve low weight, the axle shaft 1 is formed into the form of a hollow cylinder. The axle shaft 1 is rotatably supported by a double row tapered roller bearing 3 (which serves as a rolling bearing) at the interior diameter of a journal box 2 (which serves as a housing and does not rotate even at the time of use). The double row tapered roller bearing 3 comprises an outer ring 4 and a pair of inner rings 5, which are arranged concentrically with each other, and a plurality of tapered rollers 6, 6. Of these elements, the entirety of the outer ring 4 is formed into a substantially cylindrical shape, and outer ring raceways 7 are formed in two rows along the inner circumferential surface of the outer ring 4. Each outer ring raceway 7 has a tapered concave geometry and is inclined such that the interior diameter of the outer ring raceway 7 becomes greater toward the edge of the outer ring 4 with reference to the axial direction thereof.
Each of the pair of inner rings 5 is formed into a substantially cylindrical shape, and a tapered convex inner ring raceway 8 is formed along the outer circumferential surface of each inner ring 5. The inner rings 5 are arranged at the interior diameter of the outer ring 4 and concentrically with the outer ring 4 while the smaller-diameter-side end faces of the respective inner rings 5 are mutually opposed. Moreover, a plurality of the tapered rollers 6, 6 are rotatably retained by a retainer 9 provided between each outer ring raceway 7 and the corresponding inner ring raceway 8.
The outer ring 4 of the double row tapered roller bearing 3 is fittingly retained by the interior of the journal box 2. In the illustrated example, the outer ring 4 is sandwiched from either side with reference to the axial direction of the outer ring 4 between a step 10 formed at a position on the interior surface of the journal box 2 close to one edge thereof (i.e., the left-side edge of the journal box 2 shown in FIG. 59) and an unillustrated presser ring fittingly fixed to the interior of the other edge portion of the journal box 2 (i.e., the right-side edge portion of the journal box 2 shown in FIG. 59). The inner rings 5 are fitted around in a position on the outer circumferential surface of the axle shaft 1 close to one end thereof (i.e., the left end of the axle shaft 1 shown in FIG. 59) with a spacer 11 being interposed therebetween. An annular member 12 called an oil thrower is fitted around a portion of the end section of the axle shaft 1 projecting beyond; i.e., to the outside of, the inner ring 5 with reference to the axial direction thereof. The inner end face of the inside inner ring 5 butts against a stepped surface formed in an intermediate section of the axle shaft 1. Accordingly, a pair of the inner rings 5 are not displaced toward the center of the axle shaft 1 (i.e., a position close to the right side in FIG. 59) as compared with the status of the inner rings 5 shown in FIG. 59. By means of a nut 14 screw-engaged with an external thread 13 formed in the outer end section of the axle shaft 1, the annular member 12 is pressed against the outer end face of the outside inner ring 5. A locking ring 16 is fastened to the outer end face of the nut 14 by means of bolts 15, 15. Projections formed along the inner periphery of the locking ring 16 are engaged with a groove formed in the outer circumferential surface of the outer end section of the axle shaft 1, thereby preventing loosening of the nut 14.
A seal case 17 is formed from a metal plate, such as a mild steel plate, so as to assume a substantially cylindrical shape overall and a crank-shaped profile in cross section. The seal case 17 is fastened fittingly to the interior of each side of the outer ring 4. A seal ring 18 is provided between an inner circumferential surface of each seal case 17 and an outer circumferential surface of the corresponding annular member 12, thereby sealing an opening on either end of a space having the tapered rollers 6, 6 provided therein. This construction prevents leakage to the outside of grease for lubrication purpose sealed in the space and entry of extraneous matter, such as rainwater or dust, into the space from the outside.
An encoder 19 is formed from magnetic metal, such as a steel product, so as to assume an overall disk shape and an L-shaped profile in cross section. The encoder 19 is fixedly coupled concentrically with the axle shaft 1 by means of a plurality of bolts 20, 20. Projections and depressions are alternately formed at uniform intervals in the circumferential direction of and in the outer brim of an outwardly-flanged disk section 21, thereby alternately varying the magnetic characteristic of the outer brim at uniform intervals in the circumferential direction.
A cover 22 is fixed to one end of the journal box 2, to thereby seal an opening at that end. The cover 22 is formed from synthetic resin or metal material and into an overall cylindrical shape having one end closed. The cover 22 comprises a cylindrical portion 23; a bottom plate portion 24 closing an opening at one end of the cylindrical portion 23 (i.e., the left-side opening of the cylindrical portion 23); and an outwardly-flanged mount section 25 provided along an outer circumferential surface close to the other end of the cylindrical portion 23 (i.e., the right-side end of the cylindrical portion 23 shown in FIG. 59). The mount section 25 is secured to one end face of the journal box 2 by means of unillustrated bolts while the other end of the cylindrical section 23 is fitted to the interior of one end of the journal box 2 and the mount section 25 butts against one end face of the journal box 2, whereby the cover 22 closes an opening at one end of the journal box 2.
A sensor mount hole 26 is formed at a position on the cylindrical portion 23 opposing the outer brim of the disk section 21 of the encoder 19 with reference to the diametrical direction thereof, so as to penetrate from the outer circumferential surface of the cylindrical section 23 to the inner circumferential surface thereof in the diametrical direction of the cylindrical section 23. A rotation speed sensor 27 is inserted into the sensor mount hole 26. A detecting section provided at the end face of the rotation sensor 27 (i.e., the lower end face of the sensor 27 shown in FIG. 59) is positioned so as to oppose a detected section provided along the outer brim of the disk section 21, with a minute clearance therebetween.
Another sensor mount hole 28 is formed at a position on the intermediate section of the journal box 2 situated around the outer ring 4. A temperature sensor 29 is inserted into the sensor mount hole 28.
In the case of the sensor-equipped rotating support apparatus having the foregoing construction, When at the time of operation the encoder 19 rotates along with the axle shaft 1 having wheels fixedly supported thereon, the projections and depressions constituting the detected section of the encoder 19 alternately pass by the neighborhood of the detecting section provided at the end face of the rotation speed sensor 27. Consequently, the density of magnetic flux flowing through the rotation speed sensor 27 varies, thereby changing output from the rotation speed sensor 27. In this way, a frequency at which output from the rotation speed sensor 27 changes is proportional to the rotation speed of the wheels. Accordingly, so long as output from the rotation speed sensor 27 is delivered to an unillustrated controller, the rotation speed of the wheels can be detected, thereby enabling appropriate skidding control of a railroad vehicle.
If an extraordinary rise has arisen in the rotational resistance of the double row tapered roller bearing 3, for any reason such as skewing of each of the tapered rollers 6, 6, and the temperature of the double row tapered roller bearing 3 has risen, the temperature sensor 29 detects the rise in temperature. In this way, a temperature signal detected by the temperature sensor 29 is also delivered to the unillustrated controller, and the controller issues an alarm, such as illumination of an alarm lamp provided at a driver's seat. In the event such an alarm has been issued, the driver takes measures, such as effecting an emergency stop.
In the case of a rotating support apparatus of conventional structure which has the foregoing construction and operates in the manner set forth, the rotation speed sensor 27 and the temperature sensor 29 are independently and fixedly supported on the cover 22 and the journal box 2, respectively. Hence, acquiring signals from the sensors 27 and 29 requires performance of a cumbersome task, as does mounting of the sensors 27 and 29. More specifically, the rotational sensor 27 is secured to the cover 22 by means of a plurality of bolts 31a, 31a penetrating through a mount flange 30a. A harness 32a serving as a conductor for acquiring a signal output from the rotation sensor 27 acquires a signal. The temperature sensor 29 is secured to the journal box 2 by means of a plurality of bolts 31b, 31b penetrating through another mount flange 30b, and a signal is acquired by way of a harness 32b. 
Because of such a construction, the space to be occupied by the sensors 27, 29 increases, and amounting operation becomes troublesome. Further, routing of the harnesses 32a, 32b also becomes cumbersome. Another consideration is addition, to the rotating support apparatus for a railroad vehicle, of an acceleration sensor for detecting vibrations, along with the rotation sensor 27 and the temperature sensor 29. Further, there is a tendency toward an increase in the number of sensors to be incorporated into the rotating support apparatus. If the number of sensors increases, the problems set forth will become more noticeable.
In the case of the above-described related-art construction, a signal output from the rotation speed sensor 27 and a signal output from the temperature sensor 29 are processed independently of each other, and no consideration has been given of processing these signals in a linked manner. More specifically, a detection signal originating from the rotation speed sensor 27 is utilized solely for detecting a rotation speed of wheels, whereas occurrence of an abnormality in the double row tapered roller bearing 3 has been determined by use of only a detection signal originating from the temperature sensor 29. For this reason, the reliability of detection of an abnormality cannot be ensured sufficiently. The reason for this is that, in the case of a rolling bearing unit, such as the double row tapered roller bearing 3, incorporated into a rotating support section of a railroad vehicle, wheels do not constantly rotate at a given speed, and hence heating due to seizure loss of the rolling bearing unit is not effected constantly. In other words, even a normal rolling bearing unit is susceptible to constant temperature variations, for reasons of variations in rotation speed. Therefore, difficulty is encountered in determining occurrence of an abnormality in the rolling bearing unit on the basis of only temperature variations.
When occurrence of an abnormality in the rolling bearing unit is determined from only the detection signal output from the temperature sensor 29, a temperature threshold value to be used for determining occurrence of an abnormality must be specified by means of taking, as a reference, a time of high-speed running during which a temperature rises. Consequently, there may arise a possibility that an abnormality arising during low-speed running cannot be detected. In view of the situations, a preferably-conceivable measure to enhance the reliability of detection of an abnormality in a rolling bearing unit is to make a determination in consideration of factors other than a temperature.
Occurrence of such a problem is not limited to a rotating support section for supporting railroad wheels; such a problem also occurs in a rotating shaft of industry machinery of various types, such as a rolling mill, or in a rotating support section of another type of machinery.
Further, in an environment in which a bearing apparatus of an industrial machinery or automobile is used, external noise stemming from a high-frequency power source or electric motor affects a circuit constituting the sensor, thereby deteriorating the accuracy or resolution of a signal output from the sensor. When the sensor is used while being attached to hardware connected to the ground of an AC power supply via a housing of the hardware, if the housing is incompletely grounded, a voltage originating from the AC power supply is also applied to the case of the sensor fastened to the housing. In association with application of the voltage, a feeble electric current flows into the sensor, and as a result noise stemming from the frequency of the electric current is superimposed on a signal output from the sensor.
In this case, the influence of external noise can be diminished to a certain extent by means of a filter or arithmetic operation.
Additionally, the temperature sensor of the related art to be incorporated into an axle bearing for detecting an abnormality, such as seizing up employs, e.g., an NTC thermistor (negative temperature coefficient thermistor) having a negative temperature coefficient. The NTC thermistor has a negative temperature characteristic (i.e., a characteristic of a resistance value diminishing with an increase in temperature), and hence, as shown in FIG. 62, a resistance value decreases logarithmically with increasing temperature. Hence, when a temperature detected by the NTC thermistor is converted into an output voltage Vt by means of a circuit such as that shown in FIG. 61, there is produced an output voltage Vt such as that shown in FIG. 63. The output voltage Vt does not change linearly with respect to temperature. When an output voltage is converted into a temperature, the output voltage Vt is subjected to analog-to-digital conversion. A resultant value is converted into a temperature through software by means of a microcomputer. Alternatively, there is a necessity of changing the output voltage Vt so as to assume a linear characteristic by means of a linearizing circuit, thereby resulting in complication of circuit configuration and an increase in cost.
Moreover, as shown in FIG. 64, a sensor unit 246 includes a circuit board 243 having a detecting section 241 and a circuit component 242 for processing a signal detected by the detecting section 241. The circuit board 243 is inserted into a case 244, and a clearance between the circuit board 243 and the case 244 is filled with hard resin (filler) 245 and the resin is cured (molded). A flange 247 is formed on an outer surface 244a of the case 244 and can be fastened to a bearing or bearing apparatus with bolts.
However, when the circuit board 243 is fastened to the inside of the case 244 through mere molding, difficulty is encountered in orientating, in a certain direction, the circuit board 243 having mounted thereon the detecting section 241 and the circuit component 242. Hence, even when a single object is measured through use of sensors 246 manufactured in the same manner, resultant measurement results disperse. Consequently, the finally-produced sensors 246 must be calibrated (or corrected) one by one.
In the case of a bearing apparatus equipped with such a sensor 246, there is a necessity of calibrating the sensor 246 as well as calibrating mounting of the sensor 246 on the bearing apparatus. Consequently, when the operating status of the bearing apparatus is evaluated on the basis of the result of measurement performed by the sensor 246, difficulty is encountered in determining whether the measurement result is ascribable to the sensor or to the bearing apparatus.
When respective linear expansion coefficients of the case 244, the resin and the circuit board 243 are different from each other, a difference arises in the amount of thermal expansion in accordance with the change of temperature. Hence, when the sensor 246 is used in the environment where temperature changes arise repeatedly, a flaking arises between the case 244 and the resin 245 or between the resin 245 and the circuit board 243. Further, a stress is exerted on the detecting section 241 and the circuit component 242, which are mounted on the circuit board 243, thus posing a risk of impairing the life of these components.
Molding process involves heating for hardening the resin. 245 or consumption of a long period of time until the resin is completely hardened; for example, a process of leaving a mold to harden for a whole day and night. In the case of resin of reactive type involving addition of a hardener, a time required for hardening is shortened. However, heat is generated, which may impart damage to the detecting section 241 and the circuit component 242 mounted on the circuit board 243.